“The number of ACL reconstructions that occur annually are on the rise, particularly in high school and adolescent aged athletes,” lead study author Mohsin S. Fidai, MD, said at the annual meeting of the American Orthopaedic Society for Sports Medicine. “About 70% of these are accounted for by noncontact injuries, the majority of which occur during jump landing. A number of risk factors that have previously been implicated in ACL injury include genetics and anatomy, but a modifiable risk factor is landing biomechanics.”

In 2005, researchers led by Timothy E. Hewett, PhD, determined biomechanical measures of neuromuscular control that might pose certain athletes to be at risk for ACL injury, particularly knee abduction and dynamic knee valgus during a drop-jump test (Am J Sports Med. 2005;33[4]:492-501). “Historically, these studies have required the use of sophisticated computer technology, which can be cumbersome from a time and cost perspective,” said Dr. Fidai, a third-year orthopedic surgery resident at Henry Ford Health System, Detroit.

In a more recent analysis, researchers validated a field-based drop vertical jump screening test for ACL injury (Phys Sportmed. 2016;44[1]:46-52). The sensitivity was 95%, the specificity was 46%, and it had a strong inter-rater reliability (k = 0.92; P less than .05).

The purpose of the current study was to evaluate the effect of fatigue on ACL injury risk using a field-based drop-jump test. “We hypothesized that fatigue would lead to greater dynamic knee valgus during a drop-jump test,” Dr. Fidai said. “We also wanted to identify individual characteristics which may place athletes at increased risk for ACL injury.”

The researchers recruited 85 athletes who competed in track and field, basketball, volleyball, and soccer. More than half (55%) were female, and the mean age was 15.4 years. They excluded athletes with any previous or current lower extremity injuries or neuromuscular deficits. Each athlete performed a maximum vertical jump, followed by a drop-jump test.

“We then fatigued all of our athletes with a standardized high-intensity fatigue protocol, and had each athlete perform another maximum vertical jump and drop-jump test,” Dr. Fidai said. “All drop-jumps were video recorded and sent to a number of orthopedic surgery residents, athletic trainers, and physical therapists for review.”

Of the 85 athletes, nearly half (45%) showed an increased risk for ACL injury after high-intensity aerobic activity. In addition, 68% of study participants were identified as having a medium or high risk for injury following the aerobic activity, compared with 44% at baseline. “When looking at fatigue, it seems to have a dose-dependent response,” Dr. Fidai noted. “In the group of athletes with higher levels of fatigue, there is a significantly increased risk, compared with their counterparts with lower levels of fatigue.”

Specifically, 14 of the 22 athletes who demonstrated over 20% fatigue showed an increased ACL injury risk. Subgroup analysis revealed that female athletes and those older than age 15 were more likely to demonstrate an increased injury risk.

“The findings of this study advocate for changes to current neuromuscular training programs to incorporate fatigue resistance, as well as to raise awareness amongst physical therapists, athletic trainers, coaches, and athletes about the effect of fatigue on ACL injury risk,” Dr. Fidai concluded. “We can target vulnerable athletes, particularly female athletes, in an effort to negate some of those effects.”

The study’s principal investigator was Eric C. Makhni, MD. Dr. Makhni, an orthopedic surgeon in West Bloomfield, Mich., disclosed that he is a paid consultant for Smith & Nephew and that he receives publishing royalties from Springer. Dr. Fidai reported having no financial disclosures.